The long-term objective of the proposed studies is to further extend our understanding of the molecular bases for the initiation and development of the mammalian dental organ. Recently, at least 20 different transformation-specific genetic elements have been found to be normal constituents of most, if not all, eukaryotic genomes. Although many of these genes have been shown to be expressed in a variety of malignant neoplasms, as well as in whole embryos, little if any data exist to identify or clarify the non-neoplastic role(s) of the oncogenes with respect to any single, well-defined developing system. Because the initial histological and proliferative aspects of mammalian toothbud development are reminiscent of neoplastic behavior in the adult, we intend to explore odontogenesis as a likely site for genetically programmed, physiologic "oncogene" expression. We intend to dissect tooth germs from a variety of pre-natal developmental stages of rat embryos, beginning with the earliest evidence for invagination of the primitive oral epithelium. Fist, organs will be reacted for in-situ hybridization against a variety of radiolabeled, oncogene DNA probes representing most of the currently described transforming genes. Second, the extent of physiologic oncogene expression will be correlated with ongoing extracellular matrix composition cell replication, migrations, keratin biosynthesis, and phenotypic differentiation. Third, the expression and appearance of "oncogene"-specific polypeptide gene products will be determined by polyacrylamide gel electrophoretic and blotting methods. Next, the major macromolecular constituents of the matrix, especially laminin, fibronectin, and Type IV collagen will be probed by immunologic detection methods to determine whether "invasive embryologic dental epithelium behaves in a manner comparable to invasive epithelial cells of malignant tumors. Finally, we intend to isolate the DNA from odontogenic epithelium and mesenchymeactively expressing oncogene-specific products. The oncogenic potential of these nucleotide sequences will then be determined following application in an in-vitro oncogene bio-assay method. In this manner, we hope to demonstrate for the first time, unequivocal evidence for programmed, non-neoplastic expression of genetic information currently associated with malignant disease. These studies will greatly enhance our current knowledge regarding the role(s) of the apparently ubiquitous transforming DNA resident within the genomes of all vertebrate cells.